#include<stdio.h>
int main()
{
	char killer = 'A';
	for (killer = 'A'; killer <= 'D'; killer++)
	{
		if ((killer != 'A') +( killer == 'C' )+( killer != 'D' )+ (killer == 'D') == 3)
			printf("%c", killer);
	}
	return 0;
}